142 



BOTANY 



The carpogonium in the Gigartinales is the end-cell of a short branch which 

 is buried in the thallus (Fig. 110, C), but the trichogyne projects above the sur- 

 face, so that it may be fertilized. After fertilization the carpogonial cell comes 

 into contact with a neighboring cell (Auxiliary cell) from which the spores are 

 developed. About the mass of spores a more or less definite wall is formed, the 

 whole constituting the cystocarp. 



Order III. Rhodymeniales 



This order is the largest, and includes the majority of the most 

 beautiful species. In these the carpogonium, as in the last order, 

 is the end-cell of a special branch, which is united with the auxiliary 

 cell (or cells), and often with the beginning of the cystocarp-wall, into 

 the so-called Procarp. This is seen in its simplest form in the genus 

 Callithamnion (Fig. 112, D). 



One of the cells of the filament sends out a short branch of two cells, the upper 

 one developing into the carpogonium with its long trichogyne (D, t). On each 

 side of the carpogonial branch is found a large cell (a;), which after the fertiliza- 

 tion of the carpogonium divides into two cells, a large upper one, which becomes 

 the auxiliary cell, and a smaller basal one which develops no further. The car- 

 pogonium, after it is fertilized, divides into two cells (E, c), and from each of 

 these a small cell is cut off on the side in contact with the auxiliary cell, into 

 which its nucleus passes, but does not fuse with the nucleus of the auxiliary cell, 



which remains passive, although 



A & ^ Q the cell is stimulated into very 



active growth. In the divisions 

 which follow and gradually 

 transform each auxiliary cell 

 into a mass of spores, the nuclei 

 all come from the repeated 

 division of the nucleus which 

 came from the carpogonium, so 

 that the spore-nuclei are the 

 direct descendants of the fertil- 

 ized carpogonial nucleus. There 

 are thus formed two masses of 

 spores on opposite sides of the 

 cell from which the carpogo- 

 nium was developed. 



The common genus Poly- 

 siphonia may be taken to 

 represent the more special- 

 ized reproductive organs of 

 the Rhodymeniales. 



Antheridia and procarps 

 are borne upon the hairs, 

 which grow from near the apex of the shoot. 



The hairs which bear the antheridia (Fig. Ill, A) are forked, and one of the 

 branches develops into the antheridium, while the other grows into a slender 



FIG. 111. Polysiphonia sp. A, tip of branch 

 with young antheridia, 6 (X 500). B, older an- 

 theridium : /, from without ; II, optical section ; 

 x, apical cell. C, ripe antheridium ( X 250) . 



